Bacteria in the wild seldom find themselves in conditions that promote efficient and robust growth. Short periods of nutrient surplus give rise to even longer periods of nutrient limitation. When deprived of nutrients or otherwise favorable conditions, many bacteria attempt to adapt by deploying strategies to acquire alternative carbon and energy sources either by activating secondary catabolic pathways and transporters or by unleashing cytotoxic compounds, including antimicrobials, to ward off competition and scavenge for resources. Many of these adaptive responses are coincidently harmful to humans. The CodY protein is the master nutrient sensor and transcriptional regulator responsible for controlling the expression of this adaptive program in low G+C gram-positive bacteria, including a number of recalcitrant human pathogens. This application aims to determine how CodY processes multiple input signals for controlling transcription on a global level to alter important aspects of central metabolism. In addition, research proposed in this application will define the physiological importance of altering CodY activity under different growth conditions, and will identify additional coeffectors of CodY. The broad goal is to elucidate the molecular mechanism by which CodY functions to activate and repress transcription at numerous loci. The projects described herein take a multidisciplinary approach using genetics, biochemistry, molecular biology and structural biology to address biological questions from a variety of directions. Reporter fusions, quantitative RT-PCR and microarrays will provide local and global expression data in vivo. In vitro techniques including gel mobility shift assays, DNase I footprinting, partial proteolysis, and in vitro transcription will confirm and complement in vivo data. Collaborations with experts in X-ray crystallography (Professor Anthony Wilkinson - University of York) and bacterial physiology (Uwe Sauer - ETH, Zurich) have been established to increase the breadth of research and discovery. Dissecting this complex regulatory network and studying the physiological consequences of disrupting genetic and metabolic circuitry underlying CodY activity will reveal how bacteria decide to activate developmental and adaptive programs. Recent work has documented genes encoding virulence determinants as direct targets of CodY-dependent repression. As such, methods and bioactive compounds that can increase the capacity of CodY to maintain repression of virulence determinants can lead to new ways to control and prevent illnesses of microbial origin.